While the present improvement has many uses it has special utility in connection with determining vehicle wheel alignment characteristics. Heretofore, means to determine wheel alignment has in many instances moved in the direction of optical systems in which light beams and measuring scales are employed, or has moved in the direction of all mechanical systems. The essence of these systems is that the alignment apparatus employs either an optical or a mechanical reference from which alignment measurements are taken.
The optical system usually employs mirrors and graduated scales upon which a light beam projected from the vehicle's wheels is read by the operator or the light beam is intercepted by photo-electric sensors whose signals are converted into alignment information. When direct reading scales are used, operation is limited by the level of ambient light. Under high ambient light conditions the scales may not be able to be read at all. The use of photo-electric sensors minimizes these problems but makes the equipment much more expensive.
In mechanical reference systems, a physical member is attached to the wheel mounted sensors which establishes the measurement reference. This member may either be a rigid bar extending between the sensors or extending to some external support, or it may be some type of elastic band stretched between the sensors rigid members. Systems using a rigid member tend to be cumbersome and slow in use, and the weight of the various members in such systems tend to put undue stress on instruments which are attempting to make very precise measurements. Elastic bands, while inexpensive, lightweight and easy to use, have two drawbacks. The instruments to which they are attached must be very low torque and the readings are adversely affected by air currents blowing against the elastic band.